The invention relates to the field of rolling bearings with information sensors equipped with an assembly for detecting rotational parameters such as the angular position, the direction of rotation, the speed and the acceleration.
Such rolling bearings with information sensors can be used, for example, to control electric motors.
The detection assembly consisting of a sensor unit and an encoder element provides the motor control system with all the information it needs, particularly the rotational speed and the position of the poles of the stator with respect to those of the rotor.
In this type of rolling bearing with information sensors, the sensor is arranged in a unit secured to the non-rotating race of the bearing, while an encoder element secured to the rotating race of the bearing rotates past the sensitive part of the sensor so as, in collaboration with the latter, to generate a signal that represents the rotation of the rotating element, it being possible, for example, for the sensor/encoder assembly to be of the magnetic type or alternatively of the optical type.
In electric motors, the rolling bearings used are generally of the rigid ball bearing type. These are bearings with a single row of balls arranged between two raceways in the form of toroidal channels, one raceway being formed on the outer race and one raceway being formed on the inner race. A cage keeps a uniform circumferential spacing between the balls. Two seals are mounted, one on each side of the bearing, to prevent any ingress of contaminants into the bearing and to keep the lubricant inside the latter.
The seals generally comprise a metal armature coated with elastic material (rubber, elastomer, etc.) intended to form a static seal with the race on which the seal is fixed and a rubbing dynamic seal with the other race. The static seal which also serves to fix the seal to one of the races is generally in the form of an annular lip or of a bulge projecting radially with respect to the periphery of the armature of the seal. The seal is fixed by forcing the annular bulge into an annular groove formed in the race, generally the outer race.
The dynamic seal is generally in the form of one or more annular lips which come into rubbing contact with bearing surfaces formed on the other race of the bearing, generally the inner race of the bearing, between the raceway and a radial lateral face of said race.
Document FR 2 678 329 describes a sealing set-up for an information sensor suited to a sealed rolling bearing. According to that document, the inner race has an interior cylindrical bearing surface adjacent to a lateral face and onto which is force-fitted a metal armature onto which a part, made of synthetic material and forming the encoder, is overmolded. The outer race has an annular groove adjacent to a lateral face axially on the same side as the encoder and into which is fixed the sensor unit which comprises a metal armature and a part made of synthetic material with an annular bulge of a shape that complements that of the groove so that it can be fixed, with sealing, into said groove.
However, this type of set-up does not allow the use of bearing surfaces that have identical shapes and sizes for the rubbing bearing surfaces of the dynamic sealing lips of each seal. The problem is that, on the detection system side, because there is very little axial space available, the encoder element is mounted on a short cylindrical bearing surface formed on the rotating inner race, the lip of the seal starting from the sensor unit bearing against the metal armature of the encoder. The inner races have therefore to be designed and machined especially for this application, which prevents the use of less expensive standard races which are mass-produced and widely used for sealed rolling bearings of the xe2x80x9cISOxe2x80x9d series, which have no means of measuring rotation parameters.
Furthermore, producing the dynamic seal by the rubbing of a lip against a sheet metal armature prevents the use of a dynamic seal of highly complex shape which provides a high level of sealing, something which is needed in certain cases. In addition, the surface of the armature that is in contact with the sealing lip may have a geometry that experiences some degree of spread from one bearing to another. There may therefore be, in this area, the risk of grease leaking from the inside of the bearing to the outside. Finally, the gap between the encoder and the sensor is not protected against the bearing lubricant, something which is unacceptable in the case of the use of an optical sensor.
Now, it is essential, for bearing life reasons, particularly for applications operating at relatively high temperatures and speeds, that the bearing has effective seals that make it possible to retain, with a minimum of friction, the grease initially packed into the bearing.
It is an object of the present invention to overcome these drawbacks.
It is an object of the present invention to propose an instrumented rolling bearing with a high level of sealing and which is economical to produce.
The rolling bearing device according to the invention is of the type comprising an outer race, an inner race, at least one row of rolling elements arranged between two raceways of the outer and inner races, means of sealing between the outer and inner races, an information sensor assembly comprising a non-rotating sensor unit supported by the non-rotating race and an encoder element comprising an annular support and an active part, said encoder element being mounted on the rotating race via the annular support, the active part of the encoder element being arranged axially on the outside of the rotating race. Additional sealing means are provided on the information sensor assembly side to isolate said assembly from the inside of the bearing by collaborating with the rotating race in a zone lying axially between the active part of the encoder and the rolling elements.
The additional sealing means may be in direct contact with a bearing surface of the rotating race.
In one embodiment of the invention, the annular support of the encoder element comprises an armature comprising a radial portion coming into contact with an external radial face of the rotating race. The radial portion of the armature of the encoder element may be welded to said external radial face of the rotating race.
In one embodiment of the invention, a cylindrical portion meets the radial portion and extends axially toward the outside of the rotating race, said cylindrical portion supporting the active part of the encoder.
In one embodiment of the invention, the armature of the encoder element comprises a second cylindrical portion meeting the radial portion and extending axially toward the inside of the rotating race, the second cylindrical portion being mounted on a cylindrical bearing surface of the rotating race.
Advantageously, the device comprises a seal supported by the race to which the sensor unit is fixed and in rubbing contact with the race to which the encoder element is fixed, said seal being mounted on the opposite side to the additional sealing means.
Advantageously, the additional sealing means and the seal mounted on the opposite side and supported by the race to which the sensor unit is fixed each have at least one sealing lip, the two sealing lips being identical.
Advantageously, the additional sealing means and the seal mounted on the opposite side and supported by the race to which the sensor unit is fixed each collaborate with a bearing surface of the rotating race, the two bearing surfaces being identical.
The additional sealing means and the seal mounted on the opposite side and supported by the race to which the sensor unit is fixed may each comprise an armature, the two armatures being identical.
Advantageously, the race to which the sensor unit is fixed has two annular grooves, each formed on one side of said race, one accommodating the sensor unit and the other accommodating a seal.
In one embodiment of the invention, the additional sealing means are supported by the sensor unit. The additional sealing means may be attached to the sensor unit, or may consist of a radial extension of the sensor unit of which they form an integral part. The additional sealing means may be supported by the non-rotating race of the bearing.
Advantageously, the race to which the sensor unit is fixed comprises two annular grooves, each formed on one side of said race, one accommodating the seal on the opposite side to the sensor unit, the other groove accommodating the additional sealing means. The additional sealing means may consist of a seal identical to the one supported by the non-rotating race of the bearing, on the opposite side to the sensor unit.
In one embodiment of the invention, the armature of the encoder element comprises a second radial portion meeting the cylindrical portion supporting the active part and directed toward the sensor unit so as to afford protection by creating a narrow passage.
In one embodiment of the invention, the outer and inner races are symmetric with respect to a radial plane passing through the centers of the rolling elements.
Thus, the encoder is mounted on the rotating race, completely away from the bearing surface zone of the seal. It is therefore possible to enjoy good dynamic sealing, for example sealing identical to that of an uninstrumented standard bearing. This arrangement also makes it possible to use standard races, standard sealing armatures and standard sealing lips, hence giving a substantial saving in terms of manufacture or purchase and in terms of stock control.